Influence of amount of shear reinforcement and its post-yield response on the shear resistance of reinforced concrete members

The minimum amount of shear reinforcement to be provided in reinforced concrete members has been a topic of debate and research for decades without reaching a consensus. Defining such values is however instrumental to build in an economic manner and to safely ensure the applicability of the models used for design or assessment. This paper presents the results of an investigation addressed at the activation and contribution of shear reinforcement to the resistance, particularly when low amounts are arranged. The research comprises an experimental part, where 10 tests are performed on full-scale beams with varying amounts of shear reinforcement and different mechanical properties of the reinforcement. The tests were instrumented with refined measurement techniques such as digital image correlation and fiber-optic measurements, allowing for a detailed tracking of the strains in the concrete and the reinforcement. The results of the program clearly show that the transition from strain localization with a single shear crack to distributed cracking is influenced by both the ratio of shear reinforcement and its post-yield response. The results are confirmed by the analysis of a comprehensive database of 236 specimens collected from the literature, where the influence of the different parameters is analyzed. Finally, it is discussed how such findings can be implemented into codes of practice, explaining the recent changes introduced in prEN 1992-1-1:2021 (draft for the 2nd generation of Eurocode 2) and fib MC2020.